The announced cuts from January (BRU, KBP and TLV) free 9 daily slot pairs in LHR (although one of these is 2210-2300 - arguably not a prime slot).
The new LHR-GVA will take 6 slot pairs (but only two of the new departures - 0700 and 1640 - and one of the arrivals - 1600 - are anywhere near (within 30 min of) the newly freed-up slots). So there must be a lot of shuffling of other route schedules going on. And at least two slot pairs must be going somewhere else (any additional Star Alliance flying announced from LHR from January, other than GVA?).